Wiring Camper Trailer to Car

You will be ok with the set up as you describe in the vehicle.
However I would seriously consider the twin charge unit as made by Arid, this will then charge the batt in the trailor to it's full capacity then pulse it.
The Fridge in the trailor needs the 12v pickup before the Twin charge unit.
I have used these chargers in two vans and highly reccomend them.
Have a look at,

www.12volt.com.au
or
www.allabout12volt.com

Being electronically challenged, I use simplicity as my great ally ! I have a rotronics controller hooking the main battery to the aux. I then parallel the aux battery down to an anderson plug at the rear (there is a curcuit breaker in that + wire of course), via your aforementioned heavy wire. The trailer came with an Anderson to connect on to the car. So after I start up, the alternator charges both the aux and the trailer battery when it pops over. Its not verr "smart" but its been working ok to date. There are, as you will see in the posts, smarter methods for achieving optimum charging of all 3 batteries, but they are too hard for me to get the gist of. I'm going toward a small gennie in the near future, so that will fix any top-ups required.

hi guys
in answer to your problem i have put the fridge in the vehicle not in the trailer this means you go on trips while leaving the trailer or camper and the vehicle charges the batery that runs the fridg
snailbait

hi alan s wa
i have purchased a generater in Sydney whis is a two stroke .85 kw for $149 .00
This does 240 volt for .85 kw or 12 volt
but i Found another brand at bunnings for $99.95 which does the same thing
this is deemed at 65 decible but TWO stroke not 4 stroke Thes are throuw away items but they are cheap
snailbate

Alan, forget the trailer plug connection and the dash switch idea, keep it simple and use the Anderson plug, but use THICKER cable to the Aux battery in the Trailer, the same size as used between the dual batteries used in the car battery system, yes, use actual battery cable, to avoid voltage drop at the rear battery!!

Connect the new trailer battery direct to the SECOND battery under the bonnet, both (+) and also (-) cables. The SECOND battery will presently be isolated from the Starter battery by your battery "smart" isolater and PLEASE use a decent FUSE between the trailer battery and the SECOND battery.

(Quote) I have a ARB dual battery solenoid that I used before upgrading to the SMART solenoid so I was going to mount this under the bonnet near the "SECOND BATTERY" and connect the + wire to the anderson plug through it.(end quote)
Is the smart solenoid capable of the job asked of it?

NOTE;
Use only ONE QUALITY battery isolator system, one that's rated as suitable for the job, use the SAME size and type of battery in the trailer as the SECOND battery, as they will in effect be actually wired in parallel (if I understand your post)